This is fairly tricky, but it is possible to do if you iframe in the form. Have you looked at that?
Thanks for you reply. You mean drag & drop a form into landing page & then use that landing page as iframe?
I don't want to use drag & drop feature. I am using form HTML source code in my landing page & I need code to put in source code for prepoulating it.
It is a bit risky, as we might change this in the future (it isn't a stable, published API), but it seems possible.